The present invention relates to tape cassette.
More particularly, the present invention is concerned with a tape cassette provided with a device for ascertaining the speed of the tape in the cassette.
In order to guarantee a high quality of recording and reproduction in cassette tape recorders the speed of the tape in such recorders has to be adjusted with a great deal of precision. However, to ensure the precise adjustment of the speed of the tape one has first to precisely determine the actual speed of the tape.
It is known to play on the recorder a tape which was recorded with a known constant frequency. The frequency obtained during playing such a tape is then compared with a predetermined standard frequency on an oscillograph. One can use, for example, a tape recorded with a frequency of 50 Hz to compare the obtained frequency (i.e. the frequency obtained when playing such a tape) with the main frequency of 50 Hz. However, such an arrangement is comparatively expensive and the process of measuring the speed of the tape with such an arrangement is very time-consuming.
It has also been suggested to determine the speed of the tape by means of a stroboscope disc. The stroboscope disc is provided in alternating sequence with white and black areas. In this case a light source flashes at a predetermined constant frequency and beams light upon the rotating disc. The light source may be a fluorescent strip lamp or a flashing lamp. If the rotational speed of the stroboscope disc is such that the time interval between two successive light flashes corresponds to the angular interval of adjacent white areas on the stroboscope disc (or to a multiple thereof), then the disc appears to be stationary. Should such relationship deviate from that discussed above (i.e. should the rotary speed become smaller or greater) then the stroboscope disc appears to move slowly in the one or the other direction.
The stroboscope effect is generally known for determining rotational speed. In the case of a tape recorder, the stroboscope disc is mounted directly on a playback shaft of the tape recorder. Obviously, should the playback shaft not be readily accessible, such an arrangement for measuring the speed of the tape becomes extremely complicated. On the other hand, different tape recorders obviously have different playback shafts of different diameters. Thus, though the peripheral speed of the playback shafts may be the same, the rotational speed of the same may vary significantly. Therefore, each stroboscope disc can be used only with one playback shaft having a particular diameter.
In order to measure the speed of the tape with a single stroboscope disc on various tape recorders having playback shafts of different diameters, it may be advisable to operatively connect the stroboscope disc directly to the tape to be tested so that the latter rotates the stroboscope disc. However, for this purpose it is necessary to conduct the tape, driven by the tape recorder, around a roller connected with the stroboscope disc. Such a constructive measure is very complicated even in the case of reel-to-reel tape recorders; in the case of cassette tape recorders it becomes almost impossible since the tape runs completely within the enclosed tape cassette.